We discovered that integrin av3 directly binds to FGF1. We developed an FGF1 mutant (Arg-50 to Glu, R50E) that is defective in integrin binding but still binds to FGF-receptor or heparin. R50E was defective in inducing FGF signaling while it binds to heparin or FGFR, suggesting that integrin binding to FGF1 is required for FGF signaling (Mori et al., 2008). Notably, R50E blocked cell proliferation and migration induced by wt FGF1 (dominant-negative effect). Furthermore, R50E markedly suppressed the growth of DLD-1 colon cancer, Met-1 highly metastatic breast cancer, and MIN-O pre-cancer lesions in vivo in pilot studies. We identified several critical defects in R50E that may be directly related to its inhibitory action: 1) wt FGF1 induced the FGFR-FGF-integrin ternary complex, but R50E did not; 2) wt FGF1 induced Tyr phosphorylation of the integrin 23 cytoplasmic domain, but R50E did not; and 3) wt FGF1 induced sustained ERK1/2 activation, but R50E did not. We thus proposed a model in which integrins are recruited to the FGFR-FGF complex through the direct binding to FGF, and this will lead to Tyr phosphorylation of 3, and ERK1/2 activation. R50E does not recruit av3 to the FGF-FGFR complex, and thereby the subsequent signaling events are blocked. OBJECTIVES: Our goal is to analyze the role of integrins in FGF signaling, to re-evaluate the current models of FGF signaling using R50E, and to establish that FGF-integrin interaction is a novel therapeutic target in cancer and angiogenesis. SPECIFIC AIMS: SA #1) Identify the role of the direct binding of integrins to FGF in FGF signaling. a) Identify the relative contribution of integrin-FGF interaction and integrin-ECM interaction to FGF signaling using cells that are suspended on poly-HEMA-coated surface. b) Analyze the role of direct binding of integrins to FGF1 in FGF signaling using newly identified candidate small-molecular-weight FGF1 antagonists. c) Identify integrins that are involved in FGF signaling in hematopoietic cells that do not express av3. d) Analyze the specificity of R50E to FGFR isoforms and kinetics of inhibition. SA #2) Test the hypothesis that R50E suppresses tumor growth in breast cancer by suppressing tumor initiation, progression, and angiogenesis using a genetically engineered mouse breast cancer model. a) Analyze the effect of R50E on FGF signaling in Met-1 cancer in vitro. b) Analyze the effect of R50E on tumor progression, angiogenesis, and microenvironment in vivo using Met-1. c) Analyze the effect of R50E on the tumorigenesis of precancerous MIN-O lesion in vivo. d) Analyze the effect of R50E on the initiation and progression of tumor and tumor angiogenesis in vivo using a genetically engineered mouse model of breast cancer, (Tg(MMTV-PyV-mT)). EXPECTED RESULTS: The proposed experiments will identify the role of integrins in FGF signaling, evaluate the potential of R50E to tumor initiation and development in vivo, and identify target cell types for R50E in vivo. The information obtained will enhance our understanding of FGF signaling and integrin-FGFR crosstalk and will help in designing a new therapeutic strategy for cancer and inflammation. PUBLIC HEALTH RELEVANCE: We discovered that FGF1 binds to integrins, and developed a mutant of FGF1 that does not bind to integrins. We found that the mutant is not only defective in inducing signals but also suppress FGF signaling induced by wt FGF1 in a dominant-negative fashion. We will address the hypothesis that the direct binding of FGF to integrins is required for FGF signaling, and analyze the inhibitory effect of dominant-negative mutant on tumor initiation, progression, and angiogenesis in transgenic mouse model of cancer.